The invention relates to an electrically conductive linoleum-based floor covering (hereinafter also referred to as linoleum floor covering). By adding at least one derivative of imidazole, imidazoline, benzimidazole or morpholine, particularly at least one cationic compound with a quatemary nitrogen atom of at least one derivative of imidazole, imidazoline or benzimidazole, the linoleum floor covering is made electrically conductive or anti-static.
The production of linoleum has been known for a long time and is carried out by first mixing all components such as linoleum cement, at least one filler and at least one coloring agent in a mixing unit, e.g., a kneader, rolling mill or extruder, to form a matrix that is as homogenous as possible. Typical fillers are wood flour, ground cork, chalk, kaolin, heavy spar and the like. The mixed mass usually contains at least one coloring agent such as a pigment, e.g., titanium dioxide, iron oxide, zinc oxide or other common coloring agents based on inorganic and organic dyes. A typical linoleum composition contains, based on the weight of the wear layer, approximately 40% by weight binder, approximately 30% by weight organic fillers, approximately 20% by weight inorganic mineral fillers and approximately 10% by weight coloring agents. The mixed mass can furthermore contain common additives such as processing agents, antioxidants, UV stabilizers, slip additives and radical initiators or also siccatives that are selected dependent on the binder.
To produce a one-colored linoleum covering, the mixed mass thus obtained is supplied to a rolling mill and, under pressure, at a temperature of typically 10xc2x0 to 150xc2x0 C. (depending on the formula and the process technology) is pressed onto a backing material. The backing material may be a material based on natural and/or synthetic fabrics or knits as well as textile materials. For example, jute fabrics, mixed fabrics of natural fibers, such as cotton, viscose staple fiber and the like, can be used.
When the mixed mass is pressed onto the backing material, the rolling mill is adjusted to produce 2 to 6 mm, particularly 2 to 4 mm, thick webs of floor covering.
The mixed mass, as described above, may be pressed directly onto the backing, which produces single-layer floor coverings. However, the mixed mass may also be supplied to a rolling mill without simultaneously feeding a backing fabric. The backing-free linoleum strip, which is referred to as sheet, can then be pressed onto a single-layer linoleum covering by a calender or by presses. These are then referred to as multi-layer (here: two-layer) coverings. The formulation composition of the two layers is substantially identical, only the pigment composition can vary.
If a color-pattemed floor covering is to be produced, differently colored, granulated mixed masses or matrices are mixed and subsequently supplied to a rolling mill and then pressed.
Since the linoleum floor covering sheets thus obtained still do not have adequate tensile strength and compressive strength, they are dried in a subsequent maturing process in maturing chambers at a temperature of about 40xc2x0 to 100xc2x0 C., typically 60xc2x0 to 80xc2x0 C., for a period of a few days up to several weeks. This causes the binder further to cross-link and gives the material the desired tensile and compressive strength.
For further details on linoleum production, reference is made to Ullmann, Enzyklopxc3xa4die der technischen Chemie [Encyclopedia of Industrial Chemistry], 4th Edition, Volume 12, pp. 24 and 25.
A disadvantage of prior art linoleum is that due to its relatively high leakage values (RA greater than 1011 Ohm) it cannot be used in rooms the functional principles of which require that the floor covering must have certain electrical leakage values, e.g., operating rooms and computer rooms. For this type of application, it is known that the electrical leakage resistance of the linoleum floor covering can be reduced by adding electrically conductive fillers, e.g. special carbon blacks and metal powders. This has the drawback, however, that the wear properties are impaired by the corresponding additive. Color design options are also greatly reduced.
DE 34 16 573 C2 (DLW AG) therefore describes conductive, antistatic linoleum sheets that have been made electrically conductive by adding derivatives of imidazoline, imidazole or morpholine. These additives are added to the linoleum formulation in amounts of up to 15% by weight. The conductivity agent added in accordance with DE 34 16 573 C2 can be added to the linoleum mass in liquid form or as a liquid preparation. Viscous agents are partly absorbed by the filler used, such as wood flour or aluminum hydroxide and titanium dioxide. Nevertheless, the mixed mass has a different Theological quality than a regular mixed linoleum mass without any addition of conductivity agent. In other words, the mass thus obtained smears more than a normal xe2x80x9cdrierxe2x80x9d mass. Due to this xe2x80x9csmearingxe2x80x9d the desired pattems are difficult to achieve. For this reason, 2.0 mm thick linoleum sheet products have thus far not been offered, only 2.5 mm or thicker.
A further problem arises since acceptable maturing times should be achieved despite this addition of liquid conductivity agent to the mixed mass. For this purpose, radical initiators, inter alia, can be used as maturing promoters. Due to the particular nature of some of these radical initiators, however, thermal stress can cause a strong odor on the machines as well as in the finished linoleum, which is undesirable for well-known reasons.
Thus, it is the object of the present invention to provide a suitable linoleum sheet as a floor covering that has low electrical leakage resistance RA ( less than 108 Ohm) but avoids the aforementioned defects of the state of the art and achieves acceptable maturing times for the linoleum floor covering sheets without the addition of radical initiators.
This object is attained by the subject characterized in claim 1.
Advantageous embodiments of the invention are set forth in the subclaims.
In the context of the present invention, it has been shown that by adding kieselguhr to the linoleum mass, the mixed mass becomes less smeary and the rheological properties can therefore be clearly improved. By adding kieselguhr, the maturing time of the sheet product was reduced and the maturing process in the maturing chambers was achieved in a period of approximately 1 month/4 weeks. On average, the maturing time is reduced by approximately 1 week compared to the state of the art; in individual cases, however, the absolute maturing time was up to 7 weeks and was reduced to 4 weeks by adding kieselguhr.
The addition of kieselguhr makes it possible to eliminate the addition of radical initiators since the added kieselguhr already sufficiently reduces the maturing time. Eliminating the radical initiators thus also eliminates the odor nuisance during the production of the linoleum sheet, particularly when the mixture is heated prior to processing, as well as at the customer""s location.
Thus, the invention relates to a linoleum-base electrically conductive floor covering with a content of an additive enhancing the conductive and antistatic properties of the covering. The covering contains as an additive at least one derivative of imidazole, imidazoline or morpholine, preferably a cationic compound with a quatemary nitrogen atom. Such derivatives are known per se as antistatic agents (cf. DE 34 16 573 C2).
Examples for compounds that may be used in accordance with the invention are:
1. Imidazole derivatives of the formula: 
where:
R is an aliphatic group, particularly an alkyl group with 6 to 30 C atoms;
R1 and R2 are hydrogen atoms, alkyl or hydroxy alkyl groups, particularly alkyl or hydroxy alkyl groups with 1-5 C atoms and
Axe2x88x92 is an anion, typical for cationic surface-active compounds.
Typically, R can represent, for example, an alkyl group with 12-18 C atoms, R1 and R2 are methyl or ethyl groups and Axe2x88x92 represents a group of the formula xe2x88x92OSO3R3, where R3 is an alkyl group with preferably 1-5 C atoms, or represents a halogen atom.
2. Benzimidazole derivatives of the formula: 
where R, R1, R2 and Axe2x88x92 have the meaning indicated above. Typically, R represents a group of the formula xe2x80x94C17H35, R1 and R2 are methyl groups and Axe2x88x92 represents an anion of the formula xe2x88x92OSO3CH3. 
4. Quatemary morpholine derivatives of the formula: 
where R, R1 and Axe2x88x92 have the aforementioned meaning.
5. Imidazoline derivatives of the formula: 
where R, R1, R2 and Axe2x88x92 have the aforementioned meaning. Typically, R represents, for example, an alkyl group with 12-18 C atoms, R1 is a methyl group, R2 is a group of the formula xe2x80x94C2H4OH, and Axe2x88x92 represents a chloride ion.
The required amount of the compound or compound mixtures used in accordance with the invention depends on the formulation of the corresponding linoleum quality and on the moment when it is added.
The inventive antistatic agent is preferably incorporated at the earliest possible moment to obtain a homogenous distribution of the antistatic agent. The amount of the antistatic agent to be added in this case is preferably between 0.5% and 15% by weight in relation to the total formulation.
In the context of the present invention, it has been shown that a linoleum floor covering with the desired electric conductivity (leakage resistance RA of  less than 108 Ohm) can be obtained as follows:
The mixed mass of the components required for the linoleum floor coverings is produced in the same way as before. In addition, 0.5% to 30% by weight, preferably 3% to 5% by weight, kieselguhr is added to the linoleum mass together with the other dry fillers. The added conductivity agent (derivative of imidazole, imidazoline or morpholine) is absorbed by the fillers during the mixing process, particularly by the1 kieselguhr, so that the mixed mass is less smeary. The addition of radical initiator was dispensed with entirely. The floor covering had an electrical leakage resistance RA of  less than 108 Ohm. The maturing time of the linoleum sheet was reduced by approximately 1 week. According to the invention, sheet product with a thickness of 2.0 mm and a standardized patterning can be achieved.
1 Translator""s note: this change merely relates to the gender of the noun kieselguhr. 
The floor covering according to the invention consists of at least one single -layer sheet that is applied to a backing material, e.g., jute. The floor covering, however, can also consist of two-layer or multi-layer sheets that are applied to the backing material.
In a special embodiment of the invention, the linoleum sheet includes an underlay of corkment.
In another embodiment of the invention, in so-called cork linoleum, cork granulate is used as filler.
The sorption agent used according to the invention is kieselguhr (frequently also referred to as silica). The SiO2 content is at least 70%, preferably 71-93%. The kieselguhr used is natural kieselguhr (fresh or salt water) and may comprise both calcined types and types that are simply dried. With respect to the absorption properties, kieselguhr""s oil absorption is at least 100% by weight, preferably 125% to 230% by weight and its water absorption at least 125% by weight, preferably between 150% to 280% by weight.
In a particularly preferred embodiment of the invention, a kieselguhr type consisting of natural saltwater diatomaceous earth with a Si02 content of 74% and a BET surface of 50.7 m2/g is used. The oil absorption of this specific kieselguhr type is 125% by weight, water absorption is 150% by weight.
Since kieselguhr is a natural product, fluctuations are relatively large depending on the locality where it is found as well as the degree and type of processing.